Most motor vehicles conventionally comprise an internal combustion engine to provide propulsive power, in combination with an electric battery for the purpose of starting the engine, and also to provide electrical power for auxiliary functions whilst the engine is not running.
It is also now common practice to provide motor vehicles with crash detector arrangements configured to activate safety devices such as, for example, air-bags or seat-belt pre-tensioners in order to provide protection to the occupants of the vehicle in the event of a crash involving the vehicle. Such crash detector arrangements typically comprise one or more crash sensors in the form of accelerometers in combination with an electronic control unit configured to receive and process the signals from each sensor and to issue an actuating command to activate an occupant safety device in the event that the signal received from the crash sensor meets certain criteria indicative of a crash.
In view of increasing concerns over the environmental impact of motor vehicles powered by internal combustion engines, there is now increased interest and importance in providing so called “cleaner” motor vehicles which produce less pollution in the form of gases which are deemed harmful to the environment. Accordingly, it is now becoming more and more common to provide motor vehicles which are powered electrically, at least during periods of their operation. For example, it has been proposed to provide electric vehicles which are driven by a large electrical motor drawing its power from a rechargeable battery.
It has also been proposed to provide so-called “hybrid” motor vehicles which typically combine a very fuel-efficient and “clean” internal combustion engine with an electric motor. Hybrid vehicles of this type are configured to be driven by the electric motor whenever possible or convenient, but are driven by the internal combustion engine when the propulsive power offered by the motor is insufficient to meet the instant performance demand, for example because the demand simply exceeds the performance limits of the electric motor, or because the source of electrical energy from which the motor draws its power contains insufficient charge. In such an arrangement, the motor typically draws its electric power from a large capacity rechargeable battery arranged to charge from an alternator connected to the engine when the combustion engine is running. However, it has also been proposed to provide electric-drive arrangements in which the motor draws its electric power from a series of high-capacity capacitors rather than from an electrochemical battery as such. The term “battery” as used in this patent specification is therefore intended to refer to any electrical energy storage device including, but not limited to, an electrochemical battery, a capacitor, a super-capacitor, etc.
As will be appreciated, electrically powered vehicles, and so-called hybrid vehicles of the general type described above require relatively large batteries, in order to provide sufficient electrical power for the propulsive motor. Accordingly, such batteries are typically configured to be very high voltage (typically approximately 300V) and to store a very significant amount of electrical energy (typically between 2-10 kWh), and as such represent a significant electrical hazard, particularly in the event of the vehicle being involved in a crash, or an internal short-circuit occurring within the battery. Additionally, batteries of a type suitable for use in electric or hybrid vehicles presently contribute very significantly to the overall cost of the vehicle. For example, it is not uncommon for the battery unit of such a vehicle to account for 10-30% of the total cost of the vehicle. It is therefore desirable to protect the battery unit from damage in the event that the vehicle is involved in an accident, thereby facilitating less-expensive repair of the vehicle.
As will be appreciated, batteries of the type described above can become extremely hot in the event of a short-circuit occurring either internally, or externally as a result of a crash, and hence represent a risk of fire or explosion in such circumstances. Another concern with high-energy electrical arrangements of this type is that damage caused to a motor vehicle in the event of an accident can cause parts of the internal circuitry of the vehicle to become damaged and expose live wiring which presents a shock hazard for the driver and passengers of the vehicle, and also to any rescue personnel in attendance.
There is therefore a need to provide modern motor vehicles with safety arrangements configured to make render the vehicle's battery safe in the event of an accident occurring.
It is an object of the present invention to provide an improved safety arrangement of a type suitable for use in a motor vehicle having an electric battery and an occupant safety device.
Whilst the invention described herein is particularly suitable for use in vehicles having a large capacity battery to power a propulsive motor, it should be noted that the application could also be used in a motor vehicle with a relatively small capacity battery provided to start an internal combustion engine.
Accordingly, the present invention provides a safety arrangement for a motor vehicle having a battery and an occupant safety device, the arrangement comprising a crash sensor responsive to acceleration, a battery sensor arranged to monitor a battery parameter indicative of the condition of the battery, an actuator for activating the occupant safety device, and a control unit operable to receive and process signals from both the crash sensor and the battery sensor, the control unit being operable to issue an actuating command to the actuator to activate the occupant safety device in response to a signal from the crash sensor.
Preferably, the safety arrangement comprises a second actuator for activating a battery safety device; the control unit being operable to issue an actuating command to said second actuator to activate the battery safety device upon receipt of both: i) a signal from the or at least one said crash sensor exceeding a predetermined threshold value, and ii) a signal from the or at least one said battery sensor satisfying a predetermined criterion.
Conveniently, said control unit is operable to perform a step of processing said signal from the battery sensor in accordance with an algorithm effective to calculate the rate of change of said battery parameter.
Advantageously, said control unit is operable to perform a step of comparing said calculated rate of change value to a predetermined rate of change threshold value, said predetermined criterion being met when said calculated rate of change value exceeds the rate of change threshold value.
Preferably, said control unit is configured to perform said steps of processing and comparing in response to the receipt of a signal from the crash sensor exceeding said predetermined threshold value.
Conveniently, said control unit is configured to perform said steps of processing and comparing in response to the receipt of a signal from the battery sensor representative of said battery parameter exceeding a predetermined battery parameter threshold value, and the control unit being operable to issue an actuating command to said second actuator to activate the battery safety device in response to said calculated rate of change value exceeding said rate of change threshold value, even in the absence of a signal from the crash sensor exceeding said predetermined threshold value.
Advantageously, the control unit is configured also to compare the signal received from the crash sensor to a second threshold value, the second threshold value being higher than said predetermined threshold value, the control unit being operable to issue an actuating command to said second actuator effective to activate the battery safety device upon receipt of a signal from said crash sensor exceeding said second threshold value, regardless of the signal received from the battery sensor.
Preferably, said control unit is configured to continue monitoring the battery sensor after issuance of an actuating command to the second actuator to activate the battery safety device.
The safety arrangement may comprise a said battery sensor in the form of a gas sensor configured to detect the presence of carbon dioxide or carbon monoxide in said battery and to generate a signal indicative of the level of carbon dioxide or carbon monoxide detected.
Additionally, or alternatively, the safety arrangement may comprise a said battery sensor in the form of a temperature sensor configured to measure the internal temperature of said battery and to generate a signal indicative of said temperature. In such an arrangement, it is envisaged that the predetermined battery parameter threshold value against which the signal from the temperature sensor is assessed may be set at approximately 40° C., with temperature signals in excess of 40° C. being considered abnormal. Also, it is envisaged that in such an arrangement, the predetermined rate of change threshold value against which the calculated rate of change value derived from the temperature sensor is compared may be set at approximately 10° C./second.
The safety arrangement may comprise a battery sensor in the form of a pressure sensor configured to measure the internal gas pressure within said battery and to generate a signal indicative of said pressure. In such an arrangement, it is envisaged that the control unit may be configured to calculate a predicted pressure value according to Boyle's Law, with said predetermined battery parameter threshold value, against which the signal from the pressure sensor is assessed, being set at approximately 10% above the predicted pressure value. Also, it is envisaged that in such an arrangement, the predetermined rate of change threshold value against, which the calculated rate of change value derived from the pressure sensor is compared, may be set at approximately 5% per second.
The safety arrangement may comprise a battery sensor in the form of an electric current measuring device configured to measure the electrical current provided by said battery and to generate a signal indicative of said current.
The safety arrangement may comprise a battery sensor in the form of a discharge monitor configured to measure the rate of discharge of the battery and to generate a signal indicative of said rate of discharge. In such an arrangement, it is envisaged that the predetermined rate of change threshold value against which the discharge rate derived from the sensor is compared would be set at around 98% of the maximum value prescribed by the battery specification. A discharge rate greater than 100% of the maximum specified value for the battery would be considered representative of critical conditions in which the battery safety device should be activated.
Preferably, said control unit is electrically connected to an independent power supply, separate from the main vehicle battery, such that the control unit and associated circuitry of the safety arrangement can draw sufficient electrical power for operation after failure or disconnection of the main battery.